When Robert Neville (Will Smith) sees the mannequin he calls Fred outside on the street. It looks like the mannequin moves it's head a little bit. During that scene, a mime replaced the mannequin to try and play with people's minds when they watched that scene.

When he was in pre-production on this film, director Francis Lawrence found himself watching The Pianist (2002) with the sound off in order to not disturb his sleeping baby, and found the quiet effect was extremely moving. He then made stark silence, with limited ambient effects or musical cues, a major part of this film's process.

Warner Brothers initially opposed filming in New York because of costs and logistical challenges. However, Michael Tadross, a veteran New York production manager got the city to approve closing the Grand Central viaduct, several blocks of Fifth Avenue and Washington Square Park, albeit at night and on weekends, between September 2006 and April 2007.

While doing a press conference in Japan for the release of the movie, Will Smith accidentally revealed the ending to a collection of entertainment reporters. Warner Brothers asked the reporters and all those present to withhold the ending and the reporters all obliged without any payoff or consideration.

The studio spent an estimated $5 million for a six-night shoot in New York City involving the Brooklyn Bridge. To film in this location, the producers needed the approval of as many as 14 government agencies. The shooting required a crew of 250, plus 1,000 extras, including 160 National Guard troops in full combat gear.

In one scene in the deserted street a billboard can be seen with a large Batman and Superman logo superimposed over each other, and the date "5-15-10". This is an in-joke at the expense of screenwriter Akiva Goldsman. Goldsman did script rewrites for a "Batman Versus Superman" project in 2002. This was just one of the countless attempts to revive the Superman franchise that culminated in the release of Superman Returns (2006). It wouldn't be until 2016 that Superman and Batman would share the silver screen together in "Batman V Superman: Dawn of Justice."

In Times Square, there is a billboard for the Justice League: Mortal movie set to open May 10th, 2010. Also in the video store, posters for the live action adaptations of Teen Titans and Green Lantern (2011).

The noise from the special effects explosions used in the scenes along the East River interrupted voice recording on the Nickelodeon children's show, Wonder Pets! (2006), which has its production offices one block from where shooting of 'I Am Legend' took place.

At the New York premiere, Will Smith apologized for the disruption shooting the movie caused to the city residents. He said, "I would like to issue a public apology to the citizens of New York. There were a couple of streets we had to close off during the filming of 'I Am Legend'. I am very sorry. People were kind of upset with me."

Before it was finally green-lit with Will Smith as the lead and Francis Lawrence directing, the closest the project came to being made was in early 1998, when Warner Brothers gave an initial OK for a version starring Arnold Schwarzenegger with Ridley Scott directing. The studio's art direction and special effects workers had even begun working on a design for the apocalyptic mutant creatures. But some high-profile big-budget failures for Warners and the huge (for that time) initial budget of $125 million led to the project being put into turnaround. If the film had been made from Mark Protosevich's original screenplay, it would have differed from the 2007 version in three major ways: it was to be set in the Bay Area of California, it would have been more of an action film and less of a drama, and it would have been filmed with the intent of being R-rated.

In the last scene of the movie, Anna and Ethan are driving through the autumn countryside. This scene was filmed in West Amwell, New Jersey because in the original filming place, the leaves on the trees had already fallen off.

In the beginning while the Doctor is being interviewed about the cure for cancer, there is a news ticker at the bottom of the screen and one of the headlines is "Shaquille O'Neal to announce his retirement at the end of 2010 season".

Much of this film was shot on location in New York City's Washington Square Park during fall and winter 2006-2007, causing holiday decorations to be taken down and replaced tumultuously for over three months.

According to screenwriter Akiva Goldsman, there were plans to produce a followup film with scripts even being written around a prequel and sequel. One prequel involved the outbreak occurring during the Thanksgiving Day parade in New York City, while another focused on the human population becoming low. The latter prequel featured a trip to Washington, D.C. and an infected elephant escaping from the zoo. However, the project was effectively shelved.

Warner Bros. gained the rights to the novel by Richard Matheson in the 1970s and produced a version of it, called The Omega Man (1971), in 1971. Previous to that, Associated Producers did an adaptation in 1964 called The Last Man on Earth (1964) with Vincent Price, shot in Italy and directed by Italian Ubaldo Ragona and American Sidney Salkow. Although Matheson did not contribute to the screenplay of the 1964 film - which took a critical drubbing - he did contribute to the screenplay for this film.

There are references to butterflies scattered throughout the movie: the "God Still Loves Us" poster; when Neville was talking to Sam about the mannequin he met in the video store a butterfly is shown flying near Sam's face for about a second; at the ending the Dark Seeker makes cracks in the glass that represent a butterfly; Neville hearing "Daddy, its a butterfly!" (a quote from his dead daughter); Anna has a butterfly tattoo on her neck.

There is an alternate ending of the film where not only will Smith survives, but learned a very valuable lesson. When the monsters are attacking them, the leader stops and then makes a butterfly with his dirty hands on the window. Smith's character then sees a butterfly tattoo on the infected woman that he kidnaps to experiment on. He reunites her with the monsters and the leader passionately rubs hands with her and lets out a very pained roar. Will Smith man learns that the monsters are not human, but are capable of expressing human emotions. When this idea was completely edited out of the film and a new ending put in, many people hated it. There was then an alternate version with this ending included that was released, and many people prefer that version.

During the scene where Neville is searching the apartments, there is an article posted on one of the cabinets stating that infected dogs could come out at dusk, leading to a later scene where Neville and Sam are attacked by dogs. This explains why the Alpha doesn't also attack Neville as the Sun and not completely gone down.

All vehicles driven by the main characters are Fords. There is the Ford/Shelby GT500 Mustang that Neville drives in the beginning, the Ford Expedition he drives throughout the film, and the Ford Escape used to depart New York at the end.